In recent years, significant development work has been done in the field of ink jet printing. One type of ink jet printing involves electrostatic, pressurized ink jet, wherein conductive ink is applied under pressure to a suitable nozzle or nozzles. The ink is thus propelled from each nozzle in a stream and is perturbated to cause the jet stream emerging from the nozzle to break into drops at the perturbation frequency and at a predetermined distance from the nozzle. The stream is thus caused to break up into a train of individual drops which must be selectively charged and controllably deflected for printing or to a gutter.
Several examples of such systems exist, one example comprising electrostatic deflected ink jet such as taught by Sweet U.S. Pat. No. 3,596,275, wherein a single stream of drops are selectively charged and passed through a uniform deflection field to impact various locations on a recording medium in accordance with the charge of each drop. Thus, by applying suitable charging signals to the drops, readable printed characters may be formed on the recording surface. Another example comprises electrostatic binary ink jet such as taught by Sweet et al, U.S. Pat. No. 3,373,437. This type of system generates a plurality of jets in one or more rows, selectively charging drops with a single charge level for deflection by a constant field to an ink drop catcher. The uncharged drops continue undeflected along the original jet path to impact the recording surface and form readable printed characters.
The emphasis in such systems has been, and continues to be, on accomplishing proper character and image formation reliably and at reasonable cost.
Ultimately, ink jet printers may be employed for a variety of applications using different paper types for various types of printing. The drops of ink that impact the paper for printing form print spots that spread across and soak into various types of paper in varying degrees. Thus, current ink jet printing provides widely varying print quality for various paper types. One approach at answering the problem may be to provide an ink jet ink having a formulation such that it produces print of intermediate quality on a wide range of papers. However, no such ink is currently available. Another approach may be to limit the types of paper which are usable in the printer to those having the best interaction with to the ink being used. However, a restriction of this type may severely limit the ultimate application of ink jet printers.
Electrostatic pressure ink jet systems have been found to perform more reliably when using inks having water as the basic solvent. Hence, even though a specific type of paper and an ink may be matched, the print quality may depend upon the environmental conditions, such as temperature and humidity. A solution may be to provide an air conditioning system with the printer to ensure that printing only occurrs in a controlled environment. However, such air conditioning systems are generally both bulky and costly.
It is therefore an object of the present invention to provide an ink jet printing system for producing a more uniform print quality on a variety of paper types and in a variety of environments.